1. Field of the Invention
The present invention generally relates to a supporting structure for rocker arms for engine valves. More particularly, the invention relates to a supporting structure for a rocker arm constituting a valve-operating mechanism for valves of an internal combustion engine.
2. Description of Relevant Art
In the valve-operating mechanisms of internal combustion engines, there have been employed several varieties of rocker arms for actuation of engine valves. Exemplarily of such rocker arms is a seesaw type rocker arm rockably supported with a support shaft, one arm end thereof cooperating with a cam and the other arm end abutting on the head of a valve stem. The necessity of the support shaft in this mechanism has complicated the structure and increased the number of component parts required in addition to the shaft. Further the disposition of the cam to be present at one end of the rocker arm and that of the valve stem at the other end thereof have enlarged the total arm length, resulting in larger dimensions than desired of the valve-operating mechanism, as well as of the entirety of engine.
In this respect, there have been already put to practical use a number of end-pivot type rocker arms employing no support shafts, which were proposed exemplarily in U.S. Pat. Nos. 3,166,058 and 2,970,585 and Japanese Utility Model Publication No. 40-16482.
In U.S. Pat. No. 3,166,058, however, the rocker arm was adapted to swing on a pivot member which was pivotally engaged in a spherical concave surface of the arm, merely in a semi-sunk manner. With this structure it was discovered that in a high rotation speed region the concave surface might undesirably experience lift-off actions relative to a ball-like portion as a pivotal part of the pivot member, thereby producing noises. Additionally, other disadvantages, such as in the assembly process, were attendant this rocker arm. A particular assembly-associated problem results from the fact that this rocker arm comprised only the concave surface at its base part for abuttingly receiving the ball-like portion and was also simply brought into abutment at its distal end with the head of a valve stem, whereby the arm had a tendency to slip out of place, thus adversely affecting the assembly work.
In U.S. Pat. No. 2,970,585, a pivotal ball-like portion was held tightly in position with a spherical concave surface of a hollow bolt, leaving little freedom for pivotal motion. Further in maintenance service, removal of the hollow bolt was also required, resulting in increased inconveniency.
In Japanese Utility Model Publication No. 40-16482, the rocker arm had, for connection with a push rod, a joint part consisting of a spherical concave portion and a ball-like portion. According to this Publication, the ball-like portion was held by being enveloped, in a spherically concaving manner, within a skirt portion of an adjust screw at the side of the rocker arm. In this respect, however, there were accompanied inconveniences, such as the extreme difficulty to be found in the practice of calking the skirt portion to envelope the ball-like portion in a smoothly pivotable manner, and the impossibility of separation therebetween, which was disadvantageous for maintenance service.
With the foregoing points in mind, the present invention has been achieved.